Numerical study to investigate the influence of CNTs on delamination resistance in broken ply carbon/epoxy composites

Abstract

In fibre reinforced polymer (FRP) composite laminates subjected to low velocity impact, one of the common mode of failure is ply breakage followed by interfacial delamination at the site of ply break. Improving the delamination resistance at the interface is therefore important and the present work examines quantitative understanding of how the addition of CNTs to epoxy might enhance the resistance to such delamination at the interface. A laminate made of plies with CNT-epoxy as the matrix and carbon fibre as the reinforcement has been considered to be broken through the full width. A full three dimensional FE analysis was carried out for such a carbon/CNT-epoxy laminate for different wt% of CNTs. Resistance to delamination has been assessed by computing critical strain energy release rate (Gc ) using quadratic stress criterion (QSC) and virtual crack closure integral (VCCI). From the results, by adding CNTs to epoxy, a significant improvement in the delamination resistance could be observed. However, the improvement is till a certain specific CNT wt% and adding CNTs further leads to a significant reduction in delamination resistance. In addition, the effect of various factors such as fiber orientation of the adjacent continuous ply and resin layer thickness on critical strain energy release rate (Gc ) have been studied. The results show that Gc also depends upon the fiber orientation of the adjacent ply and on the resin layer thickness. As the resin layer thickness increases, a significant increase in Gc is observed.